1. Field of the Invention
The invention disclosed herein relates to explosive formulations with improved combustion efficiency. More particularly, the explosive formulations of the invention are capable of maintaining a relatively high blast pressure in an oxygen poor environment, such as a tunnel or other confined spaces.
2. Description of the Related Art
There is a long history of studying blast explosives, reactive metals and associated metal combustion technologies. The success of the development of Solid Fuel-Air-Explosive (SFAE) has been demonstrated providing 30–40% increased internal blast over a conventional explosive. SFAE is a singular event with combined mixing and initiation of the reaction. In confined spaces, transition to full detonation is not required for enhanced blast, if the solid fuel is ignited early in the dispersion process. A series of reflective shock waves generated by the detonation mixes the hot detonation gases with metal particles and compresses the metal particles at the same time. These actions provide the chemical kinetic support to maintain a hot environment, causing more metal to ignite and burn. This late time metal combustion process produces a significant pressure rise over a longer time duration (10–50 msec). This is a phase generally referred to as after burning or late-time impulse which can occur outside of where the detonation occurred, resulting in more widespread damage.
Aluminum has been used as the metal of choice, due to high heat of combustion, cost and availability. Billets of SFAE made with Al, provide savings in volume with increased fuel mass for blast performance. However, combustion efficiency has been an issue, especially in the event that the fuel content (35–60 wt %) is high with respect to the total weight of explosive composition. Poor combustion efficiency is often observed in many of the thermobaric warhead tests, which causes the severe ineffectiveness of the weapon. This is due to the high ignition temperature, 2200 K, typically required for proper combustion of AL. During the burning of Al, heat is produced and aluminum oxide is formed. However, the burning of all the metal to completion requires maintaining the hot environment. This environment can be best maintained if it is supported chemically by the combustion of other oxidizer species (i.e. AP or nitrate ester liquid, IPN (isopropyl nitrate)) that are much easier to ignite (AP has an ignition temperature of 250 C and IPN has a low flash point of 22 C). The combustion of these additives produce the hot gases to support the burning of metal, thus 100% combustion efficiency can be obtained. Metal composites, metal and oxidizer combined granules, produced from coating of particles with a binder, can be made easily with techniques well known in the art.
Another combined approach to further improve the metal combustion efficiency is to use a more reactive metal as part of or as the entire metal fuel component. New reactive metal materials such as nano-sized aluminum to increase the reactivity, titanium and boron alloy to increase the thermal output, and magnesium/aluminum alloy to lower the ignition temperature are among the most promising approaches to increase the metal combustion efficiency. More powerful explosives such as CL-20 that are capable of raising the detonation pressure and temperature are also extremely beneficial.
There exists a need in the art for new explosive formulations with new reactive metal and metal composites to have 50–100% higher blast energy than those by the baseline composition such as Tritonal or PBX N109. Further, the new formulations coupled with new warhead designs will have the potential to form one of the most powerful thermobaric warheads, when compared to the weapon systems that currently exist.